We are in middle to prototyping a lead free assembly for one of our customers. We are using lead free bare PCBs, consumables and components, except for two ICs which are leaded per the customer BOM. Will the overall assembly be defined as lead free per the directive, if the total lead content (of the whole populated PCB)is less than 0.1% by weight, or do we need the get the individual component to be less than 0.1% by weight?

Per part.... lookup the european ROHS rules. If you are asking this question and doing lead-free assemblies. Than you have not yet done enough homework. Read all materials on ROHS/Lead-free that you can.

One of our customers had us building "Pb-free" assemblies with a few Sn/Pb parts on them. THEY got rolling too slowly and we were not able to bring in the required Pb-free components due to lead-time (not Pb-time) issues. When they started requesting Pb-free, we told them right away that they wouldn't be able to get all their parts in the timeline they proposed...

So we had a don't ask, don't tell situation... "Please Mr. EMS manufacturer, build our assemblies and mark them Pb-free, even though you know they aren't".

It made me and the rest of the people building the product uncomfortable...

It depends on the contract. Is it they build what they are told to build or they are saying they are building leadfree.

And it's not the assembly or the part that has to be leadfree. It's the parts of the parts that have to be less than the given per centage. An IC might have less the per centage overall but if the leads which can be broken off are over, then the whole assembly using it fails ROHS.

Obviously, it is not considered the ROHS compliance product already. One or few components are not ROHS, how can it be ROHS product? If it is agreeable by your end customer, you should list down the part which are using leaded product before hand, at least both parties understand the situation, and get the waiver to ship the product.

Assuming you are going to build using a Leaded part on a Lead Free Process - beware of Weak Joints. I saw this at a large Multinational company - They had secondary reflow on a Top Side QFP when the PCB went over the wave. We did pull strength tests on the QFP Leads, and found issues. Since the only way of avoiding the heat transfere during wave would have been to mask under the QFP (not possible), we looked else where for a solution. A combination of Wave temp, pre-heat and Wave contact was not sufficient to fix - so believe it or not, the Reflow process cooling was adjusted, which changed the joint structure and stopped the secondary reflow during the later Wave Process.